Method of treating the rock, aplite



' Oct. 23, 1945. R. F. BRENNER 2,387,561

METHOD OF TREATING THE ROCK, APLITE I Filed March 26, 1945 7Sheets-Sheet 1 NGFELDSPAR l K FELDSPAR 2 Fig. l

NOIlVSNO'B SBHDNI INVENTOR. Ralph E Brznner:

ATTORNE Y5 Oct. 23; 1945.

R. F. BRENNER METHOD OF TREATING ROCK, APLITE Filed March 26, 1945 7Sheets-Sheet 2 mo E3555 SE oom INVENTOR. I Ralph EBrznnzc BY j M, W l MATTORNEYS Oct. '23, 1945. R. F. BRENNER 2,387, I VIETHOD OF TREATI NGTHE ROCK, APLITE Filed March 26, 1943 v Sheets-Sheet 3 TEMPERATURE 'FFig. 3

IVNVENTOK Ralph E Brenner.

BY M, 7 PM ATTORNEYS Oct. 23, 1945. R. F. BRENNER METHOD OF TREATING THEROCK, APLITE Filed March 26, 1943 '7 Sheets-Sheet 4 'INVENTOR. Ralph EBrenner BY I M, f

r ATTORNEYS Ogit. 23, 1945. R. F. BRENNER METHOD OF TREATING THE ROCK,APLITE Filed March 26, 1945 7 Sheets-Sheet 5 INVENTORI Ralph EBrennertBY I W W M ATTQRNEYS R. F.. BRENNER METHOD OF TREATING THE ROQK, APLITEOct. 23, 1-945. 2,387,561

'7 Sheets-Sheet 6 Filed March 26, 1945 TEMPERATURE "F Fig. 6

INVENT OR. Ralph E Brznner:

ATTORNEKS V Oct. 23, 1945. R. F. BRENNER I METHOD OF TREATING THE ROCK,AI LITE Filed March 26, 1943 7 Sheets-Sheet 7 Fig. 9

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INVENTOR. Ralph E Brenner BY Y W M +2 Fig. 16

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Patented Oct. 23, 1945 METHOD OF TREATING THE ROCK, APLITE Ralph F.Brenner, Lancaster, Ohio, assignor to Dominion Minerals, Incorporated,Washington, D. (3., a corporation of Virginia Application March 26,1943, Serial No. 480,641 2 Claims. (Cl. 241-32) ginia, has the followingapproximate chemical composition I A l I Per cent Albite (Al 90, An 10)55' Zoisite 22 Sericite s 13 Microcline Quartz 3 Titanite, garnet,apatiteand clino-zoisite 2 At the present time, considerable difficultyis encountered in grinding the rock aplite due to its excessivehardness, the lack'of cleavage, and the tendency to produce an excessiveamount of fines during grinding. In grinding aplite at the present time,a large amount of fines, finer than 200 mesh, are produced because ofthe nature of the grinding action required to reduce the extremely hardlumps into grains of suitable size. Due to the nature of these fines, alarg percentage of this material is waste material. Also, because of theextreme hardness and lack of cleavage of the 1 aplite, it is necessaryto have very rugged and wear-resistant grinding equipment, which isexpensive, and still excessive wear occurs.

As indicated in Patent No. 2,304,440, issued to Ralph F. Brenner andRoger D. Dubble, on December 8, 1942, the rock aplite has iron incombined form therein, and it is very desirable to reduce this ironcontent in order to make the aplite suitable. for useinceramic mixtures,such as in glass batches, orfor. similar uses.

One of the objects of my invention is to treat the rock aplite beforegrinding in such amanner that its resistance to grinding will bereduced, due to a change in physical structure.

Another object of my invention isto treat the rock aplite beforegrinding in such a manner that grinding will not only be facilitated butalso subsequent treatment to remove the iron content will befacilitated.

Another object of my invention is to treat the rock aplite beforegrinding in such a manner that excessive wear on the grinding equipmentwill be reduced to a minimum.

Another object of my invention is'to treat the rock aplite in such amanner before grinding that its resistance to grinding will be greatlyreduced and its physical structure changed so that the grindingoperation required to reduce the lumps of aplite to suitable grain sizewill not be of such a nature as to produce a'high percentage of fines.

Another object of my invention is to provide a complet and efiicientprocess for treating the rock aplite, as mined, to reduce it to theproper grain size and to reduce the iron content thereof.

The rock aplite, as mined, usually consists of lumps of various sizes.As previously indicated, it has been very diflicult to grind these lumpsin order to produce'grains of the proper size. I have found that ifthe'aplite is subjected to a proper calcining or heat-treating operationbefor grinding, grinding is facilitated. I have discovered that for thispurpose it is desirable to calcine or heat-treat the aplite at atemperature in excess of 1000 F. and up to the fusion point of theaplite, which usually is about 223'? F. The most effective and preferredrange of calcining temperatures is between 1650 and 2000" F. The time ofheating will depend upon the size of the lumps of the aplite. It ismerely necessary to heat the aplite for a period sufiicient for the heatto penetrate completely into the interior of the lumps. After the apliteis subjected to this heat-treatment, it is cooled in air orwaterquenched or sprayed. I prefer to either waterquench or spray theaplite.

Although I do not wish to be limited to any particular theory, thcalcining or heat-treating operation apparently changes the physicalstructure of the aplite, causing permanent expansion or dilatationthereof and fracturing preferentially along the grain boundariesthereof. This apparently is the reason for the improvement in thegrindability of the aplite and for the production of a greaterpercentage of ground material of the desired screen size.

In order to establish the grinding characteristics of aplite and toestablish the temperature at which calcination should be carried outprior to grinding, certain tests were made. Similar tests were made onother materials, such as soda feldspar, potash feldspar, and quartz, toshow that the results obtained by calcining aplite within the ,propertemperature range are caused by properties characteristic of aplite. andnot .of the individual minerals contained in the aplite.

The accompanying drawings will aid in understanding these tests and theresults obtained. In these drawings:

Figure l is a diagram showing expansion and cooling curves for aplite,soda feldspar, potash feldspar and quartz, heated at temperatures withinthe range, room temperature to 2000 F.

Figure 2 is a diagram showing curves for grindability indices plottedagainst calcination temperature obtained from various calcined samplesof aplite, soda feldspar, potash feldspar and quartz.

Figure 3 is a diagram showing curves which indicate the percentageincrease in grindability, owing to calcination, of calcined samples ofaplite, soda feldspar, potash feldspar, and quartz.

Figure 4 is a diagram showing curves in which the percentage of plus16-mesh material is plotted against temperature for the calcined anduncalcined samples of aplite, soda feldspar, potash feldspar and quartz.

Figure 5 is a diagram showing curves in which the percentage of minus'16 plus IOU-mesh material is plotted against temperature for thecalcined and 'uncalcined samples of aplite, soda' feldspar, potashfeldspar and quartz.

Figure 6 is a view wherein the curves indicate the percentage increasein minus 16 plus 100- inesh material plotted against temperature for thecalcined and uncalcined samples of aplite, soda feldspar, potashfeldspar and quartz.

Figure 7 is a reproduction of a photomicrograph of an uncalcined sampleof aplite taken under a polarizing microscope at magnifications withoutcrossed nicols.

' Figure 8 is a photomicrograph at 10 magnifications which is the samefield as Figure '7 and which was photographed with crossed nicols.

Figure 9 is a crossed nicols photomicrograph at 10 magnifications of asample of aplite calcined at 1000 Fahrenheit.

Figure 10 is a similar view of a simple of aplite calcined at 1300Fahrenheit.

Figure 11 is a similar view of a sample of aplite calcined at 1500Fahrenheit. I

Figure 12 is a similar view of a sample of aplite calcined at 1650Fahrenheit.

Figure 13 is a similar view of a sample of aplite calcined at 1800Fahrenheit.

Figur 14 is a similar view of a sample of aplite calcined at 2000Fahrenheit.

Figure .15 is a similar view of a sample of aplite calcined at 2150Fahrenheit.

Figure 16 is a photomicrograph at 1 0 magnifications which is the samefield as Figure 15 but which was photographed without crossed nicols. Toestablish the grinding characteristics of the materials in questionbefore calcination and after they had been calcined at varioussignificant. temperatures, it was decided to use the Grindability indexmethod developed by Bond and Maxson* as a means of showing changes ingrinding characteristics owing to calcination.

*In addition to tests on aplite, in this work, the effect of calcinationon grindability was studied for soda feldspar (albite), potash feldspar(microcline), and quartz. The reason for including soda feldspar,potash, feldspar and quartz in this investigation is that they are majorconstituents of aplite rock and it was desired to show that in theparticular temperature range where calcination renders aplite leastresistant to grinding, the effect :is .due to .some change which isinherent in the makeup of aplite and that cannot be accounted for by thephysical changes that take place in soda feldspar, potash feldspar andquartz.

The samples of aplite, soda feldspar, potash. feldspar and quartz usedin this investigation were. received in lumps, some as coarse as 10inches. The largest lumps were sledged down to crusher size and theneach material was carefully stage crushed to minus inch.

Table 1 which follows gives the chemical composition of the aplite, sodafeldspar, potash feldspar and quartz samples.

Table 1.Chemical composition of aplite, soda feldspar, potash feldspar,and quartz samples 1 Blank spaces indicate that no determination wasmade. Ignition gain.

The mineralogical composition of this same aplite rock has been givenpreviously. The soda Bristol, model A-116, dilatometer machine.

data obtained in these tests.

feldspar was optically identified as albite (A190,

An 10), the potash feldspar as microcline and the quartz as alphaquartz.

In order to determine whether the materials under consideration passedthrough inversion or transition points on heating and to establish thetemperatures at which calcination should be carried out prior togrinding, dilatometer tests were made. The tests were made in aRockwell- The Rockwell-Bristol dilatometer is an instrument thatmeasures dilatation or elongation with increase in temperature and plotstemperaturedilatation and time-dilatation curves.

Figure .1 presents the temperature dilatation This figure was preparedby plotting on rectangular coordinates, inches of elongation as ordinateand temperature in degrees Fahrenheit as abscissa. These four specimenswere all dilatometrically treated in the same .manner and presentingthem in one figure shows the relative expansion of aplite, sodafeldspar, potash feldspar and quartz in the range A. I. M. E. MillingMethods, 1934, pages to 145, and A. I. M. E. Milling Methods, 1939,pages 296 to'300.

roomitemperature to 2000" Fahrenheit and. the contraction as thespecimens were allowed to cool to room temperature.

The curve for soda feldspar shows that its elongation is quite uniform:until a temperature of 1650 Fahrenheit is reached, where a transitionpoint occurs and the elongation increases rapidly to six times itsprevious rate. When it reaches 1800 Fahrenheit, the elongation is sloweddown and at 1900 Fahrenheit shrinkage begins. The cooling curve isuniform and shows that soda feldspar does not pass through a transitionpoint on cooling. The vertical displacement between the beginning of theheating curve and the end of the cooling curve shows that the permanentdimensional change is slight.

The curves for potash feldspar show that it has uniform elongation withheating and that it contracts to practically its original length uponcooling. The uniformity of these curves indicate that potash feldspardoes not pass through a transition point in the temperature rangestudied.

The curve for quartz shows that it has a much more rapid elongation thaneither potash feldspar or soda feldspar and that this elongation isuniform until a temperature of about 1100 Fahrenheit is reached, wherethe curve flattens off with practically no further elongation up to1800'? Fahrenheit followed by slight shrinkage up to 2000 Fahrenheit.The chang in the slope of the quartz curve at 1100 Fahrenheitindicatesan inversion point and a change from alpha to beta quartz. It issignificant that the cooling curve passes through this same inversionpoint, 1

showing that the change is reversible and a permanent dimensional changedoes not persist.

The fact that the specimens of soda feldspar, potash feldspar, andquartz return very nearly to their original lengths warrants theconclusion that their permanent expansion caused by heating is slight. a

The aplite expansion curve shows that the elongation-is uniform until atemperature of 1650 Fahrenheit is reached where a slight increase intween room temperature and 1650 Fahrenheit and maintains this rate to2000" Fahrenheit. The

expansion curve described for aplite is similar to that describedearlier for soda feldspar but the total expansion of the aplite is threetimes greater.

The cooling curve for aplite does not parallel the heating curve forthere is no reverse transi tion at 1650' Fahrenheit and the totalcontraction is only one third of the expansion. In

marked contrast to the curves for soda feldspar, potash feldspar, andquartz the aplite retains a large permanent deformation.

Two other dilatometer tests were made on aplite the curves for which arenot shown in Figure 3. In one of these tests the maximum temperatureemployed was 1400 Fahrenheit, that is below the aplite transitiontemperature. The cooling curve came back to the starting point At 1850Fahrenheit the curve Ti assumes a rate approximately equal to that beofthe 27 test samples calcined as above.

showing that when aplite is heated below its transition point, theoperation is reversible. In the other test, the aplite was heated to2000 Fahrenheit, then cooled slowly and heated a second time to2000Fahrenheit and cooled. The curves for this test showed that the curvesfor the second heating and cooling followed the first cooling curve,starting and ending at the same point. This is added proof that apliteundergoes a permanent dimensional change when heated to 1650Fahrenheit,. but that when expanded aplite is again heated, onlyreversible changes occur.

Calcinwtion tests In view of the facts presented in Figure 1, samples ofeach of the materials were calcined at the following temperatures: 1000Fahrenheit, which is below the transition point of any of the minerals;1300 Fahrenheit, which is above the inversion point for quartz; 1500Fahrenheit, which is below the transition point in aplite and sodafeldspar; 1650 Fahrenheit, which is at the transition point for apliteand soda feldspar; 1800 Fahrenheit, which is near the middle of theaplite transition zone; and 2000" Fahrenheit, which is at the end of theaplite transition zone and the reversing point for quartz. Anothertemperature was desired in order that the maximum limit or temperaturerange in which calcining is effective would be established. This wasobtained by observing the lowest calcining temperature at whichsoftening of the aplite took place. Although the fusion point of apliteis said to be 2237 Fahrenheit, it becomes soft at 2150" Fahrenheit, sothe latter temperature was chosen as the upper limit for the calciningtests.

In the furnace used in calcining these samples, the samples were broughtto the desired temperature and. held there for fifteen minutes in aneutral atmosphere after which the calcined ma terial was removed fromthe furnace and allowed to cool inair. i

Table 2 which follows shows the average temperatures maintained for the15-minute calcination periods. Screen analyses were made of each Thesesamples were then used in the grindability tests now to be described.

Table 2.--Aoe"rage temperatures in degreesFahrenheit for fifteen minutecaicination periods Desired calcination Soda Potash temperature Aphtefeldspar feldspar Quartz Grinda bility tests Samples of the variousmaterials were used in a series of grindability tests based on themethod of Bond and Maxson to determine the relative grindabilities ofthe four uncalcined materials and to determine the eifect ofcalcinationupon their grinding characteristics.

The grinding characteristics of the samples were shown by thegrindability index which is the number of grams of finished materialthrough a given mesh produced per revolution of a ball mill. In thiswork, 16 mesh was. taken. as the Table 3.Grindability indices ofcalcined and uncaloined samples and percentage increase in grindabilityindex owing to calcination Percetage Calcination Grindability increasein Material temperature, index, grams grindability degrees F. perrevolution index owing to caleination 2. 104 100 l, 000 2. 660 126 l,300 3. 650. 173 1, 500 3. 406 162 l, 650 10. 380 493 1, 800 9. 934 4722, 000 10. 313 490 2, 150 5. 248 249 4. 617 100 1, 000 4. 719 102 1, 500(i. 594 143 1, 650 8.961 194 1, 800 9.001 195 2, 000 8. 480 184 2, 1505. 538 120 5.060 100 1, 000 5. 174 102 1, 300 5. 352 106 1, 500 5. 799115 l, 650 6. 249 123 l, 800 7. 295 144 2, 000 7. 149 141 2, 150 5 5.930 117 3.224 110 1,000 3. 362 104 l, 300 4. 092 127 l, 500' 4. 450 1331, 650 4. 420 137 l, 800 4. 326 134 2, 000 4. 330 134 2, 150 5. 139 1591 Uncaleined.

The same results are presented in graphical form in Figure 2 wheregrindability index is plotted against calcination temperatures. Thisfigure shows that in an uncalcined condition aplite is the hardest togrind, followed in order by quartz, soda feldspar, and potash feldspar.When calcined at 1000 Fahrenheit, aplite alone shows a slight increasein grindability. Between 1000 Fahrenheit and 1300 Fahrenheit there is anincrease in the grindability of the quartz, agreeing with thedilatometer data which showed the inversion from alpha to beta quartz atabout 1100 Fahrenheit. In the same temperature range the aplite curvepractically parallels the quartz curve, and there is very littleimprovement in the grindability of potash feldspar. There was notsufficient soda feldspar to make calcination tests at all temperatures,and a test at a temperature of 1300 Fahrenheit was omitted.

, At 1650 Fahrenheit, there'is an increase in the grindability of all ofthe materials except quartz which remains practically constant throughthe range 1500 to 2000 Fahrenheit. This is conclusive evidence thatheating quartz beyond 1500 Fahrenheit does not materiallyimprove itsgrindability, and it cannot be responsible for the increasedgrindability of aplite between 1650 and 2000 Fahrenheit, which isunusually marked and agrees with the transition temperature at whichpermanent deformation takes place as shown by the dilatometer data. FromFigure 2 one might be led to believe that the two feldspars wereresponsible for the increased grindability of aplite in this temperaturerange. In order to show more clearly the differences in the grindingcharacteristics, Figure 3 is given.

In Figure 3, the percentage increase in grindability is plotted againstcalcining temperature. This figure shows that in comparison with theuncalcined materials, the grindability of aplite calcined between 1650and 2000 Fahrenheit is increased 500 per cent. For the same calcinationtemperature range, the grindability of soda feldspar is increased only200 per cent, and the grindability of quartz and potash feldspar, only150 per cent. Figure 3 shows that the percentage increase ingrindability is so much greater for aplite than for any of the othermaterials that they cannot account for this characteristic inaplite.

Referring again to the data in Figure 2 it shows that although aplitewas the hardest to grind in the uncalcined condition, it was the easiestto grind after calcination inthe range of 1650" to 2000 Fahrenheit.

Size composition of grindability samples It may be thought thatcalcination alone Without grinding would account for an appreciableincrease in the fines found in the grindability samples. That this isnot the case is shown in Tables 4, 5, 6 and 'l, which follow, which givethe screen size distribution of products after calcination but prior togrinding for aplite, soda feldspar, potash feldspar and quartz,respectively.

Table 4.-Size distribution of aplite samples after calcination but priorta grinding Uncalcined 1000 F. 1300 F. 1500 F. 1650 F. 1300 F. 2000 F.2150 F. Mesh Size Wt. Cumul. Wt. Cumnl. Wt Oumul. Wt. Cumul. Wt. Oumul.Wt. Cumul. Wt. Oumul. Wt Oumul.

% wt. wt. wt. wt. wt. Wt. wt. wt.

Under the polarizing microscope; it is apparent that the toughness ofaplite may be accounted for by its massive crystalline structure and theabsence of cleavage or other natural fracture planes The photomicrographreproduced in Figure '7, which is the same field as that reproduced inFigure 8except that it was photographed without crossed nicols, showsthis clearly in that the grain boundaries are almost extinct. Even at3401 magnifications only a very few fractures at the grain boundariesare noticeable and their width does not exceed two microns.Consequently, combining the knowledge ofthe hardness of the mineralspresent in aplite and the physical structure of aplite, it isunderstandable whythe uncalcined aplite is difiicult to grind.

Figures 9, 10, 11, 12, 13, 14, 15 and 16 present photomicrographs ofthecalcined aplite samples. Those calcined to temperatures of 1000, 1300and 1500 Fahrenheit have an appearance similar to the uncalcined sampleand nearly the same grindabilitiese The samples calcined at 1650, 1800and2000 Fahrenheit showthe presence of numerous fissures andcracksthroughout the grains and along the grain boundaries. The boundaryfissures are the most pronounced, and in the main, vary from 15 to 180microns in width but somexas wide as 300 microns were seen. Thephotomicrcgraphs of the specimen calcined at 1650 Fahrenheit show thecoarse preferential fissuringaround the grains and is probably moretypical thanthe photomicrographs of the sections calcined to 1800 and2000 Fahrenheit which show the finer fissuring throughthe large grainsof feldspar present in the .aplite rock.

The extensive fissuring just cited for the calcination range 1650 to2000 Fahrenheit indicates that the expansion was great and agrees withthe dilatometer data presented in Figure 1 and the grindabilityindicesplotted in Figure 2. Thefissuring displayed in the aplite sectioncalcined at 2150 Fahrenheit is not so pronounced and sharp as in thephotomicrographs just discussed. The reason is best illustrated. by thephotomicrograph of the same field without crossed nicols which showsthat most of the black lines are isotropic glass and not fissures.Recall that at this temperature the aplite became soft duringcalcination.- Thus the fissures opened up by calcining in thetemperature range 1650 to 2000 Fahrenheit are filled with glass when thematerial is further calcined to 2150 Fahrenheit. This accounts for therapid drop in grindability at this temperature.

' The photomicrographs explain the percentage change in sizedistribution caused by calcination which is also illustrated by Figure6. The reason for the marked increase in minus 16 plus 100- mesh sizesfor calcined aplite is that the fissuring caused by calcination ispreferentially at the grain boundaries and the average grain size ofaplite is 28-mesh. Uncalcined aplite contains no fissures to speak of.

Specific gravity determinations In order to express quantitatively themagnitude of expansion caused by calcination, specific yugravitydeterminations were made.- 100. minus A inch plus G-mesh particles ofeach material Were used and the determinations were made by deslimingthe solids in water, weighing in water,

drying and weighing in air. Table 13 shows the data for uncalcined and1800 Fahrenheit calcined samples. The aplite is the only sampledisplaying noticeably a, change in specific gravity indicatingexpansion, which again verifies the dilatation and grindability data.

Table 13.-Specific gravities of calcined and 1m- Icalcined samples ofaplite, soda feldspar, pot ash feldspar, and quartz 1 Specific gravitiesMaterial O i i alcincd at Uncalcmed 18000 F Quartz .e 2. 65 2. 64

Water quenching} As previously indicated, it is desirable to waterquench the aplite immediately after calcining. This results in greaterthermal cracking and fracture of the aplite than when it is air-dried asin the previously discussed tests. In order to determine the effect ofwater-quenching after calcining, the following tests were made.

I took lumps of aplite, from two to three inches in diameter, andcalcined the aplite at a tern perature of about 175035. for a period ofminutes. Part of these lumps were then quenched in water and the otherpart was cooled in air. I then selected samples of the untreated aplite,samples of the treated and water quenched aplite and samples of thetreated and air-cooled aplite and made crushing tests on these varioussamples. Great difiiculty was encountered in crushing the untreatedaplite. On the other hand, the treated and air-cooled aplite crushedeasily and the treated and water quenched aplite even more easily.

In further tests relative to this invention, samples of the untreatedaplite and samples of aplite treated in the manner indicated above andwaterquenched were ground in such a manner that all particles would passthrough a 16-mesh screen. It was found that in the case of the untreatedground aplite 38% of the ground material passed through a ZOO-meshscreen, or in other words, 38% of the material was in the form ofexcessive fines. On the other hand, in the case of the treatedwater-quenched aplite, only 5% of the Table 14.-Capdcities obtained whendry grinding dz'fierently treated aplite in a rod mill under standardconditions gfi gg i Weight Weight Weight Weight ml feedg per cent of percent of per cent of per cent Test conditions (mud to -2048M 48100M.100200M of -200M g in ground in ground in ground in ground mesh productproduct product product Aplite calcined at 1800 F. for one-half hour,Water quenched, and dry ground 75. 2 45. 7 24. 9 12. '8 16. 6 Aplitecalcined at 1800 1. for onehalf hour, air cooled, and dry ground 50.151. 9 20. 8 11.1 16. 2

These tests definitely proved that waterquenching of the aplite aftercalcining is desirable.

Conclusion increases its grindability to minus l6-mesh, 500

per cent and improves the desirable screen size composition of theground product, minus 16 plus 100-mesh, by 150 per cent.

3. On being heated from 1650 to l800 Fahrenheit, aplite passes through atransition point and permanent deformation takes place. The deformationis one of expansion and is characterized by the formation of largefissures along the grain boundaries and to a lesser extent across themineral constituents of aplite.

4. The tests show that the results obtained by calcining aplite withinits critical temperature range are caused by properties characteristicof aplite and not accountable forby soda feldspar, potash feldspar andquartz.

5. Water-quenching the aplite after calcining will increase itsgrindability further beyond that produced by air-quenching and willresult in the production of a greateramount "of material of the-properscreen size. 7

6. Calcining and grinding the aplite in the manner described willfacilitate acid leaching to reduce the iron content in the mannerdescribed in Brenner and Dubble Patent No. 2,304,440, and will alsofacilitate magnetic separation.

Various other advantages will be apparent.

Havin thus described my invention, what I claim is:

1. The method of treating aplite to reduce it to a grain size suitablefor use in ceramic ware or for similar purposes, which comprisescalcining lumps of the aplite at a temperature sufficient to causepermanent expansion thereof, said temperature ranging from 1650Fahrenheit to 2000 Fahrenheit, and then grinding the calcined lumpaplite to a size such that all the ground material will pass through a16-mesh screen while having approximately per cent of the total weightof the ground material greater than mesh.

2. The method of treating aplite to obtain a product having a-maximumparticle size of -16 mesh and having more than approximately 80 per centof the total weight greater than 100 mesh, said method comprisingheating the aplite to a. temperature between 1650 F. and 2150 R,cooling, and grinding so that substantially all of the said aplite willpass through a -16 mesh screen while having approximately 80 per cent ofthe total weight of the ground material greater than 100 mesh.

RALPH F. BRENNER.

CERTIFICATE OF CORRECTION.

Patent No. 2,387,56 October 25, I915,

RALPH F. BRENNER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows Page 5,Table 8, third column thereof, for the numeral "LL22" read L1.5.2 andthat the ,sai d Letters Patent should be read with this correctiontherein that the same may cohform to the record of the case in thePatent Office.

Sighedand sealed this 29th day of January, A. D. 19%.

Leslie Frazer (Seal) First Assistant Commissioner of Patents.

